Spark plug with tapered spark gap

ABSTRACT

A spark plug has a shell at one end of an insulator body, a central electrode extending through the insulator body beyond the shell, and a tapered ground electrode secured to the shell and extending alongside the central electrode. The ground electrode, from its point of connection with the shell to its tip, converges gradually toward the central electrode to form a tapered gap between the electrodes. The ground electrode provides a short path for conducting heat readily through the shell to the water jacket area of the engine cylinder block. The gradually tapered gap causes the spark to travel between different points in the gap, depending upon temperature and running conditions of the engine, which reduces wear on the electrodes. The tapered gap also allows good ventilation for gases in the spark gap area thereby reducing corrosion of the electrodes.

United States Patent [191 Fernandez {541 SPARK PLUG WITH TAPERED SPARK GAP [76] Inventor: John J. Fernandez, 1620 S. Myrtle Ave., Monrovia, Calif. 91016 [22] Filed: Aug. 11,1971

[211 App]. No.: 170,885

Related U.S. Applicatlon Data [63] Continuation-impart of Ser. No. 815,538, April 14,

1969, abandoned.

[52] U.S.Cl ..3l3/l41 [51] Int. Cl ..1I0lt 13/20 [58] Field 01 Search ..3l3/l4l [56] References Cited UNITED STATES PATENTS 1,191,603 7/1916 Loose................................l..313/141 2,077,711 4/1937 Redinger.......... ..313/14l 2,129,472 9/1938 Lysholm et al... ..3l3/l4l 2,149,261 3/1939 Anderson ..3l3/14l 2,620,784 12/1952 Cipriani ..3l3/143 2,845,566 7/1958 Regar....... ..3l3/l41 2,878,299 3/1959 Stan ..l23/l69 3,317,773 5/1967 Inoue ..313/l41 FOREIGN PATENTS OR APPLICATIONS 8/1909 GreatBritain ..313/l4l 11/1924 GreatBritain ..3l3/14l [57] ABSTRACT A spark plug has a shell at one end of an insulator body, a central electrode extending through the insulator body beyond the shell, and a tapered ground electrode secured to the shell and extending alongside the central electrode. The ground electrode, from its point of connection with the shell to its tip, converges gradually toward the central electrode to form a tapered gap between the electrodes. The ground electrode provides a short path for conducting heat readily through the shell to the water jacket area of the engine cylinder block. The gradually tapered gap causes the spark to travel between different points in the gap, depending upon temperature and running conditions of the engine, which reduces wear on the electrodes. The tapered gap also allows good ventilation for gases in the spark gap area thereby reducing corrosion of the electrodes.

4 Claims, 4 Drawing Figures SPARK PLUG WITH TAPERED SPARK GAP CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application, Ser. No. 8l5,538, filed Apr. 14, I969 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to spark plugs, and more particularly to a spark plug in which the electrodes form a tapered spark gap.

Conventional spark plugs commonly used in automobile engines today have a straight central or power electrode, and a ground electrode secured to the spark plug shell adjacent to the central electrode. The ground electrode generally extends beyond the shell parallel to the central electrode, with its end portion being bent to overlap the tip of the central electrode.

This prior art electrode configuration has a number of disadvantages. For instance, the spark continuously travels between the tip of the central electrode and a fixed point at the end of the ground electrode, which continuously produces a hot spot causing the end of the ground electrode to erode during use. Moreover, the overlapping end of the ground electrode traps hot gases in the spark gap area. This creates foreign deposits of carbon and the like on the interior of the spark plug shell and the electrodes, frequently producing short circuits of the plug contacts and thus impairing the ignition system. The impaired ventilation in the spark gap area also prevents adequate cooling of the electrodes, which is a further cause of electrode erosion.

Because of the electrode configuration of the conventional spark plugs, automobile manufacturers and garage owners generally recommend that plugs be cleaned every 5,000 to 6,000 miles, and replaced every l0,000 to 12,000 miles. If most driving is done in city traffic, with numerous starts and stops, the manufacturers and garage owners recommend replacing the plugs even more often.

Some prior art spark plugs have electrodes of various shapes for producing a tapered spark gap which causes the spark to fire between different points in the gap during use. Since the spark does not continuously fire between two fixed points, as in conventional spark plugs, spark plug life is prolonged. However, the electrodes in prior art plugs with tapered spark gaps have not been designed to allow heat to be conducted readily through the spark plug shell to the engine cylinder block. Thus, hot spots tend to develop and cause excessive wear of the electrodes. Moreover, prior art tapered electrodes generally do not provide effective ventilation for gases flowing in and out of the spark gap area, which allows carbon deposits and the like to build up on the electrodes.

SUMMARY OF THE INVENTION This invention provides a spark plug with a tapered spark gap that causes the spark to travel longitudinally between different points in the gap to reduce wear on the electrodes. The configuration of the electrodes is such that they conduct heat readily to the spark plug shell and allow good ventilation for gases in the spark gap area.

Briefly, the spark plug includes a hollow shell, an insulator body in the shell, with the shell terminating in a rim portion at one end of the insulator body. A central electrode extends longitudinally through the insulator body beyond the rim of the shell, and a ground electrode connected to the rim extends from its point of connection radially inward toward the central electrode and alongside the central electrode so that the two electrodes lie in a common plane. The ground electrode terminates in a remote end spaced longitudinally from the rim and spaced laterally from the tip of the central electrode. The configuration of the ground electrode is such that it defines, from its point of connection with the rim to its remote end, a gradually tapered gap between the electrodes converging toward the remote ends of the electrodes.

In use, the gradually tapered gap between the electrodes allows good ventilation for the gases in the spark area, without trapping heat or providing surfaces which accommodate the build up of carbon deposits and the like. Moreover, the ground electrode provides a short, direct path for the immediate transfer of heat to the water jacket area of the engine cylinder block. This facilitates rapid cooling of the electrodes, which avoids the creation of hot spots and the resulting electrode erosion.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings in which:

FIG. 1 is an elevation view, partly in section, of a spark plug with a tapered spark gap;

FIG. 2 is a fragmentary sectional elevation view showing the spark plug of FIG. I in use in the cylinder block of an internal combustion engine;

FIG. 3 is a plan elevation view of the spark plug electrodes taken on line 3-3 of FIG. 1; and

FIG. 4 is a plan elevation view of an alternate electrode configuration for the spark plug of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a spark plug 10 includes an insulator body 12 for supporting an elongated central, or power, electrode 14 axially disposed in the insulator body as is well understood in the spark plug art.

Insulator body 12 is mounted in a suitable tubular metallic shell 16 and secured in it by upper and lower fluid-tight gaskets l8 and 20, respectively. The lower portion of shell I6 has an externally threaded surface 22 adapted to mate with cooperating internal screw threads in an engine cylinder block as is well known in the art. A downwardly facing circular rim 23 is formed at the bottom of threaded portion 22 of the shell. The lower portion of central electrode 14 extends in a straight line beyond lower rim 23.

The upper end of central electrode I4 is provided with a terminal portion 24 which is suitably threaded into the upper end of insulator body 12 to contact the upper end of the central electrode. Upper terminal portion 24 is capped with a binding post 26 adapted for connection to an electrical conductor (not shown) for supplying high voltage to the central electrode.

An angularly disposed ground electrode 28 is secured to lower rim 23 of shell 16 in any suitable manner, such as by welding. Ground electrode 28 extends radially inward in the plane of central electrode 14, and extends alongside the central electrode, terminating in the vicinity of the tip of the central electrode. Ground electrode 28, from its point of connection with rim 23 to its tip, converges gradually toward central electrode 14 to form a gradually tapered spark gap 30 (see FIG. 2) between the electrodes. Preferably, the portion of ground electrode 28 closest to shell 16 extends radially inward toward central electrode 14 at a faster rate than the remote end portion of electrode 28. As shown best in FIG. 2, the gap formed between the electrodes converges slightly toward the remote ends of the electrodes. This arrangement provides a gap size ranging from a minimum to a maximum distance within the range of gap sizes normally required for all automobile engines. Although the specific configuration of ground electrode 28 shown in the drawing is preferred, this electrode may be given other shapes, without departing from the scope of this invention, as long as spark gap 30 gradually and continuously converges toward the remote ends of the electrodes. Preferably, the center electrode extends not more than about five thirty-seconds inch beyond the lower end of insulator body 12. As described above, ground electrode 28 terminates substantially evenly with the end of central electrode 14. This size of the electrodes provides good dissipation of heat, as will be described in greater detail below.

FIG. 3 shows a plan view of electrodes 14 and 28. Preferably, central electrode 14 is circular in cross-section, as is the usual case in the spark plug art. Ground electrode 28 also has the usual substantially rectangular configuration, with its largest cross-sectional dimension facing the central electrode.

FIG. 4 shows an alternate tapered ground electrode 29 in which the side facing the central electrode is curved concave outwardly to match the contour of the adjacent outer surface of the central electrode. Electrode 29 is tapered continuously, in a manner identical to that shown in FIGS. 1 and 2, for the entire length of the curved surface which neighbors the central electrode. It is believed that this configuration of electrode 29 provides a broader spark than in conventional tapered spark gaps. The matching arcuate surfaces of the electrodes provide a wide electrode area in the spark gap, which reacts with the incoming fuel and air mixture to provide a broad spark. Since the sparking surface of the electrodes is increased, longer spark plug life results.

The use of spark plug is best understood by referring to FIG. 2 which shows threaded portion 22 of shell 16 engaged with an internally threaded bore 31 in a cylinder block 32 of an internal combustion engine. Cylinder block 32 has the usual water jackets 34 for cooling. The tapered gap 30 provided by the electrodes projects entirely beyond the lower extremity of rim 23 of spark plug shell 16 into an upper portion 36 of the engine cylinder combustion chamber. The configuration of the electrodes causes a spark to occur at different levels in the gap depending upon the temperature and running conditions of the engine. For example, when starting a cold motor the temperature and density of the incoming fuel and air mixture is substantially the same from one end to the other of the spark gap area. Under these conditions, the spark occurs where the distance between the electrodes is shortest, i.e., at the bottom of the gap where the spark is represented by reference numeral 38.

As engine speeds increase and the temperature increases accordingly, the spark plug insulator body and shell become heated, so that the fuel and air mixture close to shell 16 becomes rarified when compared with the cooler mixture at the top of combustion chamber 36 near the remote ends of the electrodes. As a result of the higher temperature and reduced density of the incoming gases, the resistance to the passage of the spark near the wider portion of the gap, as represented by reference numeral 40, becomes reduced when compared with the resistance at the narrower part of the gap. Thus, the spark occurs closer to the shell at the wider portion of the gap.

During operation of the engine, the spark moves up wardly in the gap, between the limits represented by reference numerals 38 and 40 as engine temperature increases. The results of the longitudinal shifting of the spark in the gap have been observed in practice. Spark plug 10 has been used in different automobile engines for several thousand miles. The appearance of the ground electrodes in all plugs used shows that the spark has travelled all along the length of the tapered gap. In one test, spark plug 10 was used for 24,000 miles in a 1967 Cadillac having an engine compression ratio of 10:]. The electrodes showed very little wear, and the wear that did occur clearly showed that the spark moved longitudinally through the gap with no one portion of the electrodes being subjected to hot spots or erosion caused by a continuous firing at one point only. Moreover, virtually no carbon deposits or the like appeared on the electrodes.

The configuration of electrodes 14 and 28 has additional important advantages. The gradually tapered gap formed between the electrodes allows the incoming gases to circulate through the gap area with a minimum of obstruction. Conversely, the ground electrode of the conventional spark plug overlaps the tip of the central electrode, which does not allow the gases to circulate freely, thereby trapping heat and the exploding gases in the space between the electrodes. The trapped gases, when exploding, create carbon deposits on the electrodes, and the trapped heat overheats the electrodes and thereby tends to increase erosion. The improved ventilation provided by the present electrode configuration allows the exploded gases to flow more readily out of the spark gap area, which substantially prevents the accumulation of carbon deposits, and enhances the heat dissipating capabilities of the electrodes.

The gradually tapered configuration of electrode 28 also permits the heat generated by the spark and exploding gases to be conducted immediately through shell 16 to the water jacket area of the engine block. Ground electrode 28 purposely does not have sharp corners, or portions which overlap other portions of the electrode. Such electrode configurations tend to trap heat in the gap area, which promotes the build up of carbon deposits and also fails to conduct heat rapidly from the spark gap area. The gradual taper of ground electrode 28 provides a shorter path for the dissipation of heat to the engine block than known prior art electrodes. That is, the continuously tapered path provided by the electrode is substantially the shortest possible distance from the spark gap to the water jacket area of the engine cylinder block. Moreover, the central electrode is short, so it also conducts heat rapidly away from the combustion area. Thus, the electrodes cool faster than prior art plugs, which tends to prevent electrode erosion and thereby provides longer life for the spark plug.

1 claim:

1. A spark plug comprising a hollow shell adapted for engagement with an engine cylinder block, an insulator body in the shell, the shell terminating in a rim portion at one end of the insulator body, a central electrode extending longitudinally through the insulator body beyond the rim portion of the shell to define a remote end spaced longitudinally from the rim, and a ground electrode connected to the rim portion of the shell and extending from its point of connection radially inward toward the central electrode and alongside the central electrode so that both electrodes lie in a common plane, the ground electrode terminating in a remote end spaced longitudinally from the rim and spaced laterally from the adjacent remote end of the central electrode, the configuration of the ground electrode being such that it defines, from its point of connection with the rim to its remote end, a continuously gradually tapered spark gap between the electrodes converging toward the free ends of the electrodes, whereby the combined configuration of the electrodes provides a short path for conducting heat readily through the shell to the engine cylinder block, causes the spark to travel longitudinally between different points in the gap to reduce wear of the electrodes, and allows good ventilation for gases in the spark gap area to reduce corrosion of the electrodes.

2. Apparatus according to claim I in which the central electrode extends beyond the rim in a straight line, and the ground electrode is inclined relative to the central electrode.

3. Apparatus according to claim 2 in which the ground electrode has a first half secured to the rim and extending radially inward toward the central electrode, and a second half integral with the first half extending away therefrom to the remote end of the electrode, the first half converging sharply inward toward the central electrode, with the second half converging slightly toward the adjacent surface of the central electrode.

4. Apparatus according to claim 1 in which the entire surface of the ground electrode facing the central electrode is curved concave outwardly to substantially match the contour of the outer circumference of the central electrode. 

1. A spark plug comprising a hollow shell adapted for engagement with an engine cylinder block, an insulator body in the shell, the shell terminating in a rim portion at one end of the insulator body, a central electrode extending longitudinally through the insulator body beyond the rim portion of the shell to define a remote end spaced longitudinally from the rim, and a ground electrode connected to the rim portion of the shell and extending from its point of connection radially inward toward the central electrode and alongside the central electrode so that both electrodes lie in a common plane, the ground electrode terminating in a remote end spaced longitudinally from the rim and spaced laterally from the adjacent remote end of the central electrode, the configuration of the ground electrode being such that it defines, from its point of connectioN with the rim to its remote end, a continuously gradually tapered spark gap between the electrodes converging toward the free ends of the electrodes, whereby the combined configuration of the electrodes provides a short path for conducting heat readily through the shell to the engine cylinder block, causes the spark to travel longitudinally between different points in the gap to reduce wear of the electrodes, and allows good ventilation for gases in the spark gap area to reduce corrosion of the electrodes.
 2. Apparatus according to claim 1 in which the central electrode extends beyond the rim in a straight line, and the ground electrode is inclined relative to the central electrode.
 3. Apparatus according to claim 2 in which the ground electrode has a first half secured to the rim and extending radially inward toward the central electrode, and a second half integral with the first half extending away therefrom to the remote end of the electrode, the first half converging sharply inward toward the central electrode, with the second half converging slightly toward the adjacent surface of the central electrode.
 4. Apparatus according to claim 1 in which the entire surface of the ground electrode facing the central electrode is curved concave outwardly to substantially match the contour of the outer circumference of the central electrode. 